Silicate gel manufacture



Patented Sept. 26, 19 33 I UNITED A E SILICATE VGEL ANUF o'rUrtE iWilliam McAfee Bruce, MountHolly," N. J., as- 1 Signor to The PermutitCompany, New York,- N. Y., a corporation of Delaware No Drawing.

This invention relates to improvements in silicate gel manufacture; anditcomprises an improved process of making a water sof ening zeolite gelin granular form from sodium silicate, and acid and alkali compounds,of; alumina,

wherein solutions of the reagents in relatively high concentrations aremixed with immediate formation of a gel and the immediately formed gelis malaxated and disintegratedin its mother 10 liquor -to which may thenbe added further batches of solutions of the reagents in still higherconcentrations withfurther gel formation, the final gel mixture beingmalaxated to a smooth uniform pulp,'this pulp being subsequently driedand washed, usually being pressed before drying; all as more fullyhereinafter set forth .and as claimed.

Base exchange silicates or Water softeningzeolites in gel form have beenmade by mixing a solution of sodium silicate, usually a commercialwaterglass solution, with a solution either of sodium aluminatepr-ofaluminum sulfate. The reagents may be in such concentrations in theirrespective solutions ,as to give upon mixture of the solutionsgelatinous precipitates, which may be jellies including all, or thegreater partoi',v the reagent liquids so mixed, a fullvolume gel orjelly beingthe result of the use of the more concentrated reagentsolutions. It has been consideredadvantageous to use solutions ofstrongenough concentrations to form jellies, but dilute enoughto permituniform admixture of the solutions before gelation.

In prior and copending applications, Serial No. 308,888,. filed Sept.27, 1928 andSerial No. 487,918, filed Oct. 10, l930,-I have describedand claimed processes of making base exchangezeolite gels by mixingsolutions of sodium silicate with solue tions both of sodium aluminateand aluminum sulfate, the reagents being so proportioned as to produce apredetermined silica ratio inthe product and to leave the mother liquoralkaline and the reagent concentrations advantageously being such as topermit completion ofthe mixing before gelation goes forward to any greatextent, the liquid mixture beingthen allowed to set into a stiff, firmjellyQ i In theart it isiusual to partially dry wet gels formed in thereagent solution mixtures, with or without pressing or filtering toremove some mother liquor, and to submit the dried gels, stillcontaining constituents of the mother liquor, to

the action of Water to produce a breakingv up and granulation. Withproper conduct of the operation, the granules formed bythedisintegrating action of water are of the-right size for .watersoftening purposes. In the art there is a tacit assumption that the gelas originally formed in the solution mixtures has 'a cellular or honey-,;comb structure equivalent to a granular struc- Application Novemberis, 1931, 1 SerialNo.'576,954

7 Claims. (01. 23-413) .j

'ture; and that this granular structure is preserved duringthe dryingoperation and appears T when the drymaterial, which may be a-press cake,is disintegrated by water."

- 'I have discovered that it is not necessary to preserve the originalstructure of the gel or jelly as formed in the reagent mixture and thatit is notnecessary to use solutions of such strength as to permituniform admixture before gelation.

I have found that excellentvvater softening gels of a rugged, granularstructure are obtained'by using solutions of relativelyhighconcentrations which causea formation of gel immediatelyupon orduring admixture and by keeping the'solutions during admixture and forsome; time thereafter incontinual agitation, .so that the 'g'ela'sformed is malaxated and its structure disintegrated to a pasty pulp.This pulped gellmay be pressed as ina filterpress or hydraulic ;.pressand-then'dried at a moderate temperature 5 in usual Ways. It mayhowever, iffdesired; be allowed-gtostand for a time and then driedwithout pressing- Usually it is economical to press outsome of themother liquor before drying. Upon treating the dry gel with Water itbreaks up into hard gr'ane ules of 'a-good size for use iria bedsoftener.

lnparticulan'l have found that the processes of myi above mentionedcopending applications are improved by using stronger. solutions, ofsodium silicate, sodium aluminate and 'aluminum sulfate, and malaxatingthe. gel as'i-formed'iand. afterformation in its mother liquor 'beforepressing and drying. The use of. more concentrated solutions has themanifest advantage of requiring less water, removal from the wet gel andas l'have found,the effect of producinga g'ranur lar rigid structure inthe-driedgel with finalfor- '95 malaxation followed by pressing' anddryinghas,

mation 'ofgranules well adapted'for continuous use in the regenerativewater softening process. The resultis a lower cost of production'withoutsacrifice of the quality of'the products} I 'T By applyingzmy improvedmethod to existing manufacturing operations it ispossible to obtain agreatly increased production from; anexisting plant. Heretofore, inmakinggel zeolites by the a threei'ea'gentfprocess it hasbeen customary,in ordertoproduce slowzgellingj mixtures of solutionspf sodiumsilicatealuminum sulfate 'and sodium aluminate; to mix. solutions. ofthese "re agents in concentrations not greater' than 4' =Baum, 6'B.- and5,B.,respectively.- In the improved method of the present inventionconcentrationsexceeding 10 B; for the" silicate,-'7 81%. for the sulfateand 6 B. for the-aluminate are possible. i

i It has-also been found that by conductinglthe vr admixing andmalaxating 'initwo or moresst'ages.

the concentrations of the solutions-admixedrin h the second stage maybe. as high as or higher than 19 Be. for the silicate, 13 B. for-thesulfate and 12 Be. for the aluminateQ Subsequent additions of thereagents in still higher concentrations may be made. the reagentsolutions, lower concentrations, such as 7 and 6 B, respectively, areused in the first step and after the gel resulting from this mixture hasbeen formed and malaxated, solutions of higher concentrations are pouredinto the malaxated pulp and'thoroughly mixed, the water of the firstmixture serving to dilute the stronger solutions 'employed'in the secondmix--v ing and malaxating step. By this two-stage procedure it ispossible to obtain a smooth malaxated uniform gel pulp from solutions ofrelatively high concentration more advantageously than bynsing the morehi hly concentrated solutions in a single stage mixture; the gel beingin the later case so dense and tough that it is difficult to reduceitsubsequently to a uniform pulp by malaxation and disintegration.

, Higher concentrations than those named above can be used but with suchhigher concentrations it is advisable to Wash the malaxated gels withwater in order toreduce the content ofsodium sulfate before pressing anddrying.

In a typical and advantageous embodiment of the present invention thefollowing solutions are made up: a (1) Sodium silicate solutionapproximately 10TB. containing per liter 22 grame NazO and 67.5 grams5102 I .(2) Aluminum sulfate solution of approximately- 1 B. containingper liter 15.8 grams A1203 and 33.8 grams S03;

(3) sodiumaluminate solution approximately ,6. B.- containing per liter29 grams A1203 and 19.7

' grams NazO.

To produce a zeolite having components in a 7 ratio corresponding to theformula NazOAIzOaGSiOz the above three solutions may be'mixed-in proportions of .1245 liters of solution (1) v7'70 liters of solution (2)and 402 liters of solution (3)) Generally speaking, it is immaterialwhether the aluminum sulfateis first mixed with the silicate solutionand the aluminate solution added or whether the aluminatesolution ismixed with the silicate solution first and the sulfate solution mixedwith the.silicate-aluminate mixture. First mixing the aluminate andsilicate with subsequent addition to this mixture of the sulfatesolutions has in most cases the advantage that relatively strongsolutions of silicate and'aluminate can be readily mixed togetherwithout formation of stiff curdsrequiring an extended time formalaxation inorder to produce a uniformly pulpe d gel. When the sulfatesolution is added to the mixed silicatealuminate solutions a gradualincrease in viscosity of the mixture occurs until about, half thesulfate is added and then, as the second half of the sulfate solution isadded, the viscosity of themalaxation mixture gradually decreases untila relatively thin, smooth, uniform pulp is obtained. When thestronglyconcentrated silicate and sulfate solutions are mixed an immediate gelformation occurs but malaxation of this gel by violent agitationus'uallypresents no great difficulty and subsequent addition of thealuminate solution with continued malaxation produces a uniformly pulpedgel. On the whole, I consider'that the most advantageous order of mixingis to first add the aluminate solution to the silicate solution aquickly with constant agitation during the addi- In a two step mixing oftion and then to add the sulfate solution slowly and with violentagitation to the pulped gel formed by malaxating the silicate-aluminatemixturee After the addition of thelast of the three reagent solutions,the agitation is continued until the gel has been thoroughly malaxatedto the condition of a smooth, uniform paste or pulp, after which thepulp is pumped to'a filterpress underv a pressure of pounds per squareinch, and subsequently the press cake,which may be about 2 to 3 inchesthick, is broken up and dried on stationary trays at a temperature ofabout- C.

for 24 hours. Upon treating the dried cake with water in the usual wayit breaks up into granules of the proper size for use in commercial,water softening. The granules are washed to remove soluble salts and arethen ready for use. They may be dried for shipment.'-

- In a second typical embodiment of the invention exemplifying atwo-stage mixing procedure, solutions of the same concentrationsas thoseof solu'-.

tions 1, 2 and-3 in the above example areusedin the first stage ofmixing; 830 liters of solution (1 being mixed with 514' liters of (2)and 268 liters of (3).

The solutions are agitated during the admixingand the gel formed ismalaxated as described in thefirst example to' produce a thin paste. Inthe second stage of mixing, the follow 1, 2 and 3 continues, 415 litersof '(4) and 134 liters of (6) maybe added" quickly and then 25'? 7liters of (5) may be added more slowly and the agitation is continueduntil the gel mixture has beenthoroughly malaxated to the condition of a120 smooth uniform" pulp. The'pulp is pressed at'a pressure of60ipoundsper square inch and the press cake is broken up,dried,'granulated and washed as in the first example.

. It is to .be noted that Whilethe total volume of the solutions-used inthe second example is thesame as the total of the solutions used in thefirst example, the total quantity ofeach of the reagents is one-thirdgreater in the second exampie then in the'first example. Consequentlythe j quantity of gel produced is one-third greater in the secondexample'than in the first; while the facilities required for mixing,agitating and malaxating are the same in both'instances.

31.6 grams Al'zosand While the agitation of the mixture of solutions Toproduce the best'product for. purposes j of a Water softening, the threereagents areproportioned as describedin-rny copending applications andaluminate being somewhat in excess of the quantity needed to'neutralize'the acid of the sulfate and to supply in addition one molNazO in the mixture for each mol A1203; the silica ratio being adjustedas desired by adjusting the proportions of alumina supplied respectivelyby the aluminum sulfate and the sodium aluminate.

t has been found usually advantageous to so cited ante, the sum of thesoda'in the silicate proportion the silicate andsulfate that a'mol of'NazO is provided for each mol AlzOa in addition to the'NazO required tocombine with theSOz of the sulfate. However some latitude in the reagentproportioning is allowable, it'being, possible with I adequatemalaxation of the gelmixture to com continued malaxation of the gel.

and reduced to a thin pasty pulp. To this pulp solutions of sodiumsilicate and of sodium aluminate in higher concentrations than those ofthe first solutions are added and the whole mass agitated to form auniform pulp. Further additions of still more concentrated reagentsolutions of the same or greater concentrations may be made with Theuniform malaxated gelpulp is then pressed and may be washed beforedrying, granulating and further washing.

I have found further that an excellent water softening silicate gel iseconomically produced by 'malaxation of a silicate-aluminate gel in itsmother liquor and by mixing with this malaxated gel pulp solutions ofsodium silicate and aluminum sulfate inrelatively high concentrationsand continuing themalaxation of the mixture. So doing, the reagentproportions can be adjusted to produce a final mixture containing anexcess of alkali and a ratio of silica to, alumina giving a ruggedproduct of high base exchange capacity with good economy in the useofmaterials. Inthis process it may be advantageous in some cases to makethe first gel from a'mixture of all three reagents and then to addsuccessive batches of silicate solution and of either aluminate oraluminum sulfate solution in concentrations greater than those of thefirstmixture and in amounts'adapted to adjust the silica ratio and-thealkalinity of the final mixture.

While I have described specifically the manufacture of gels using as rawmaterials sodium 'sili-' cate and both sodium aluminate and aluminumsulfate as sources of alumina, the invention is applicable generally togel manufacture from soluble silicates, alkaline solutions of metaloxides and non-alkaline metallic salts. I For example, potassiumsilicate may be used as a source of silica.

, and alkali for the gel; an alkali vanadate, stannate or similarcompound of metal and alkali may replace aluminate and the metal saltmay be an iron chloride or sulfate. Gels for special purposes such asfor use as catalysts or catalyst carriers may be made from a widevariety of materials.

What Iclaim is:- s 1. In the manufacture of silicate gels by mixingsolutions of sodium silicate, aluminum sulfate and sodium aluminate toform gels which are subsequently pressed .and dried, a process whichcomprises mixing solutions of the three reagents in concentrations suchas to cause gel formation immediately upon mixing, malaxating said gelin its'mother liquor during and after its forma-. tion, mixing with saidmalaxated gel solutions of said three reagents in greater concentrationsthan those of the first mixed solutions, malaxating the resulting mixedgel in its mother liquor compounds with subsequent drying of the wetmediate gel formation,flmalaxatingsaid gel in its reagents andmalaxating the gel formed in theto a uniform pulp,

cate, sodium aluminate and aluminum sulfate in volumes andconcentrations causing gel formation immediately upon mixing malaxatingsaid gel in its mother liquor during and after its formation, mixingsaidmalaxated gel with solutions of the reagents in smaller volumes andgreater concentrations than those of the first solutions, malaxating theresulting mixed gel inits mother liquorto a uniform pulp and drying andwashing the pulped gel. v I a 3. In making silicate gels from gellingmixturesof solutions. of sodium silicate andof'alumina gels, aprocess-which comprises mixing solutions of the reagents inconcentrations such as to form a gel immediately upon mixing-malaxatingthe gel inits mother liquor during and after its formation, mixing withthe malaxated gel solutions of, the reagents inconcentrationsgreaterthan those of the first mixed solutions and malaxating theresulting mixed gel in its mother liquor. I

4. In the manufacture of a silicate gel-by gela- 1 tion of mixedsolutions of sodium silicate and of' one or more compounds of aluminawith subsequent removal of water from the wet gel, a process whichcomprises mixing solutions of'the reagents in concentrations such as tocause immother liquor during and after its formation,successively'mixing with said malaxated gel solutions, ofjthe reagentsof greater concentrations than those'of the first mixed solutions and ofsuccessively increasing concentrations'and malaxk in the mother liquorating the resulting mixed gel to a uniform pulp. V p

5.; In thefmanufacture of silicategels from mixed solutions of sodiumsilicate, sodium alumi nate and aluminum sulfate, a process which com-j'prises mixing solutions of sodium silicate. and

sodium aluminate inconcentrati'ons such as 'to' form a gel immediatelyupon mixing, malaxating the gel in itsmother liquor'during and afteritsformation, mixing with the .jmalaxated gel solutions o'f'sodiumsilicate and of aluminum sulfate "v ingreaterconcentrationsthan those of,thefirst v solutions; mixedand'malaxating the gel formedinthefinalmixture." I i p '6. In the manufacture of silicate gels ,frommixed solutions of sodium silicate,'sodium alumi- .125 nate and aluminumsulfate, a process which com-l. prises mixing solutions ofthethreereagents in concentrations such as to form a gelimmediately upon mixing,malaxating the gel in its mother.

liquor during and after it formation, mixing with said malaxated'gelsolutions of sodium "silicate and of! sodiumaluminatejin'greater'concentrations than those of the first solutions ofthese I final mixture. v I

of a silicate gel by gela- I '7. In the manufacture tion of .mixedsolutions of sodium silicateand of 1 cheer more compounds of aluminawith subsequent removal of water from the wet gel, a proc-: ess whichcomprises mixingsolutions of the re-' agents in concentrations such asto cause immediate gel formation, malaxating said gel in its motherliquor during and after its formation, successively mixing withsaidmalaxated gel solutions of the reagents of greater concentrations atingthe resulting mixed gel in the mother liquor which comprises mixingsolutions of sodium sili-- Q than those of the first mixed solutions and'malax-

